Beware, Long post ahead.
(Had this idea a long time ago, died, now i'm bringing it back to life :3)

Sorry if there's any grammar mistakes, I'm copy pasting several separate paragraphs

A bit back, one of my friends and I worked really hard on an idea of ours, a second OCH, this time for commissioner ghostmane! Like a mini boss similar to seerus, the levels would be similar to OCH, except differently themed... Here is our idea:

Depth 1:
The knights spawn on an elevator landing (as always). After sifting through the arsenal station and stepping on the party button, Feron walks up to them and informs them of the situation, and then shows them the way to the front lines. Naturally, there are a few random monsters in the way, but they are all perma-poisoned. Some are perma-sleeping. Feron takes the knights to the defenses, which consist of hastily set-up turrets and hedgehogs. They are being assaulted by massive waves of scuttlebots, and the NPC knights are trying to take cover behind them while occasionally popping out to take potshots at the crowds. If the players do nothing, the NPCs will eventually take enough damage that they are "knocked down" for a period of time. Player assistance is clearly needed. Feron, for once, joins you in the fight. He always shields when under attack, and only launches an attack when enemies aren't assaulting him. If the players die, Feron can revive them, but only up to half his remaining health (just like regular knights). Once the fight is over, Feron goes around the defenses reviving stunned NPC knights, instructing the players to scout the area for gremlins. Most of the gremlins you encounter are wielding Prototype Rocket Hammers. However, if you watch carefully, you'll notice a small, unarmed gremlin at the bottom of the screen. He is trying to watch you while keeping his distance, and if you try to approach him, he'll run off. If you manage to corner him and deal him enough damage, he will stop and ask you to not kill him. Of course, you comply...right? Relieved, the gremlin gets up and shows you to a secret elevator behind a fake wall. This will take you to the next level.

Depth 2:
The players spawn in a level that is a little darker than usual. As you progress through the level, you notice a strange absence of enemies. The level is littered with the dead bodies of gremlins, wolvers, and fiends, broken zombie bodies, dead slime patches, and broken robots. Further on, there are bodies of fallen knights, each with a different wound. Some are deformed, shattered, smashed, burned, and frozen; others are unrecognizable blackened shadows of their prior forms. One can only wonder what happened here. As you pass by a patch of broken gun puppy defenses, there are a few that remain operational, but they are perma-poisoned and easily destroyed. A couple of them are Void Puppies, offering a clue as to what has happened here. You step on the party button, and suddenly swarm seed becomes visible. A dark, void-infested, barely-visible gremlin appears whom you can't identify, cries out in surprise, then vanishes, leaving a trail of Void spawn pads in his wake. The gates lock both behind you and ahead of you, and you are forced to fight the never-ending waves of the Voids. A timer appears, and you are told that the level will be bathed in fire when the timer reaches zero. There is no obvious way out. At the tenth second, however, the gates open, and you are greeted by a familiar face: that gremlin you met in the last level! He has opened the gates for you, shut off the fire trap, and got the elevator working again. You can then take the elevator to the next level.

Depth 3:
By now, the players must be wondering why the Void keeps making cameos in the levels. They will soon find out why. In this mission, the knights find themselves in an even more empty room. There are no hostiles in this room, at all. There are dead gremlin menders all over the place, unarmed mecha knights, and patches of blackness dotting the walls and corners. The ground quakes periodically, the level is dim, and it is large and complex. There are walled-in areas that are completely filled with spikes that haven't popped up yet, but watch out: if you walk onto them, a gate behind you will close and the spikes will pop up. To open the gate, you must quickly make your way over to a pot on a spawn pad, hit the switch, and get out before the gate closes again in a few seconds. It's not impossible to get out without dying, but it's hard. Then there are areas with partially-hidden flame throwers that activate when you come near; keep an eye out for them. There are areas with purple haze that curse you if you walk in it; since there are no enemies, it need not do you harm, but it's unnerving. Why are the knights wandering around in such a level? You don't really know yet. There are computer panels to read, but they contain broken messages that are difficult to read. You can examine some of the dead gremlins, but you won't find much besides dark shards or crowns upon performing an action on them. What you find in the level is: a mewkat. It will follow you once you find it, and if you lead it to the exit, the gate will open and allow you to board the elevator, but killing it will have the same effect. Also, the computer panel behind the gate will become active, allowing you to read it:

light and void at peace
a helpless mewkat can live
may someday find piece

Beast and slime, droid, undead;
The clock still ticks, so think ahead.
You have the key, just put it in,
And enter me, that light may win.

Depth 4:

The next level is a complicated beast. The knights find themselves accompanied by the gremlin, who is too nervous to walk with you. He always appears at the party buttons, though. The first part of the level is a maze of indestructible blocks, patrolled by Haze Wisps (stun-inducing wisps). If you can find your way through, you will come upon a button. Pressing it has no obvious effect. However, it actually destroyed one of the indestructible blocks, providing you an exit.

The next part is essentially another maze, but instead of walls, you have 1x1 traps. You have to predict where the next batch of traps will lower; if you fail, you get hit by spikes. If you can successfully navigate through the traps, you will be faced with a greater challenge: a floor that is all but covered in damaging tiles. A small number of them form a safe, narrow (2 tile wide) path through the floor, but it is twisted, and in order to find it, you have to play hexmines: whenever you find a land mine, you know that it is bordered by at least 1 safe tile. Just don't stay put, or the land mine will damage you.

The last area is a miniboss room belonging to a laser-firing battlepod. It fires its laser into a rotatable prism, which it can direct at knights. The knights can also turn it against the pod, however, and successive laser strikes against it coerce it into using more and more mirrors to make it harder for the knights to use it against itself. Once defeated, a gate leading to the boss is unlocked.

Entering through the above gate takes you into a large, empty party-button room. Stepping on it doesn't seem to do anything at first, but after a few moments, it becomes clear that invisible enemies have spawned. After defeating them, you hear a sinister cackle, and a gremlin slowly struts into the room. It's Commissar Ghostmane himself! He notes that he is both impressed and insulted at your successful passage through his depth; impressed that you survived, and insulted that you failed to die in his well-planned traps. If you want something done well, you have to do it yourself, so he decides to take on the challenge of fighting you. He's not a fair fighter, though, and brings in special Crimson Stalkers to assist him. Ghostmane himself is equipped with all three Lockdown powerups: a Guardian Shield, Striker Boost, and Recon Cloak. That means he can heal himself and his minions.There is a room with a battlepod. It's only weapon is a stun laser, and it fires the weapon into a prism which it can redirect at the knights. However, the knights can redirect it too, and it turns out that the pod's shield is only vulnerable to its own laser. So upon breaking the shield, a more complicated set of prisms is introduced, so it is harder each time to fire the laser at the pod. Defeating the pod allows the knights to access the boss, Ghostmane. The boss begins by cloaking and deathmarking the knights. Once they are deathmarked, he uncloaks and attacks, boosting and shield-canceling his strikes. If his cloak is broken, he will pull his shield up. Sometimes, when he's marked the players, he'll just let his stalkers attack. He can be tracked by watching his footprints. When he stops making them, you know he is about to strike. He moves in a predictable zig-zag pattern that he only deviates from when he enters a new phase. There are 3 phases. In phase 1, he just cloaks and lets the stalkers do his work. When they're finished off, phase 2 begins, and he begins launching attacks himself, in addition to those made by newly-spawned stalkers. Defeating the stalkers again or dealing the boss enough damage puts him into phase 3, where he does all the fighting himself. He will dodge and weave around attacks while cloaked, and tries to attack players from behind. If you can still defeat him, he will cloak and vanish. Upon his defeat, he drops a Mysterious Crystal. It's pitch-black, and even the brightest light doesn't reflect off of it. It's just large enough for you to carry on your back. You can't leave without it, since the gate blocking the elevator won't stay open while it isn't being carried. A void gel spawns when you pick up the shard.

Depth 5:

True fight with Commissar Ghostmane! Enter through a passageway like snarbolax, and stand on party button to begin.
Stage 1: he wanders around invisible, and death marks his opponents, but he does not attack; the spawns attack any death marked people, otherwise they just stand around. Ghostmane's death mark has no warning, it just appears suddenly. In stage 1, he will leave a trail of footprints which you must follow in order to hit him. When the footsteps stop, it means he will death mark someone. It doesn't have to be someone near him, it could be anyone, just a random person. The only time he appears is when he is death marking someone, and that's the time he is vulnerable, for about 5 seconds as he completes his death marking. Once sufficient damage is done, stage 1 will be complete.
Stage 2: spawns disappear, and three new spawns are summoned by ghostmane, who no longer can use his cloak. Ghostmane will begin lobbing "curseballs? (Think fireballs, but purple and misty-looking)" which are capable of causing curse. In this phase, Ghostmane is invincible. The three new spawns are minions of ghostmane, and they each have something different. One has a gran Faust, one has a sentenza (capable of cursing) and one has a dark retribution (capable of cursing). Once these three are dead, stage 2 will be complete.
Stage 3: ghostmane's cloak has regenerated, and now he can freely cloak and uncloak. He walks around with a shadow-curse version of the final flourish, and he attacks all the knights. He can not death mark, and his footprints never disappear, even when he is cloaked or uncloaked. In this stage, Ghostmane is invincible unless cursed. Several spawns, one of each kind of gremlin, appears. In this stage, several mirrors will appear, and a hit will cause the mirror to rotate clockwise by 45 degrees. There's a stun laser, and u need to use mirrors to aim the laser at a button at the end of the wall, which will send a signal (needs cool animation) to ghostmane's (something electric) and knock him down and curse him. The curse will last for between 5 and 15 seconds, and he will remain knocked down for 5 seconds. You will be able to damage him any time he is cursed, but he is easier to hit when he's lying down, and he can attack back when he is not knocked down. The button on the wall will shift position every time, so it will be necessary to change the array of mirrors to hit the button. The laser is activated by hitting the switch, which will send a pulse out to begin bouncing off the mirrors to reach the button. After 20 seconds, the laser will dissipate, so if the knights accidentally set an infinite loop it will disappear eventually. The laser pulse does massive normal damage, about as much as the void turrets in the unknown passage. The laser will not travel too quickly, maybe slightly below the speed of a Polaris bullet, and it reflects off the mirrors as if gravity does not affect it. After doing sufficient damage to ghostmane, stage 3 is complete.
Stage 4: ghostmane is really angry, and his anger starts pulling patches of the swarm towards him, which forms a swarm seed in the middle of the room. In this stage, the mirrors have disappeared, and you attack him as you would Jelly King, totally focused on damage. He uses his shadow-curse final flourish to its full extent, attacking the person who has done most damage to him, just like vanaduke. In this phase, just do enough damage to him to finish stage 4 and defeat him. He no longer has his cloak, but he does have a shield, and he can use shield canceling techniques so it is much more difficult to kill him. However, his shield only guards about 2/3 of him, and there is a small opening in the back which the knights must hit to do damage, in this level, cursed shadow fire appears wherever he walks every 10 seconds or so, and knights must do damage to the fire to make it go out, (purple shadow fire which can do curse but no fire). After defeating him, there's a quick cutscene and the knights go to the next floor, pick up the special mat used to craft "ghostmane's cloak (armor with 1*, 3*, and 5* variants)” and receive their prize boxes.

(Note: Ghostmane's cloak is used to compliment mask of Seerus, both currently for gunners)

Immediate prizes for finishing mission:
The loot from this quest could be a much more nerfed version of ghostmane's cursed-shadow final flourish. It's about as fast as FF, and can do curse about as much as gran Faust, but the curse is much weaker and only lasts for 10 seconds or so, and the damage done by the sword itself is very low, almost like a wild hunting blade. The other loot could be a gun, which does shadow damage and is as slow and powerful as the Callahan, although not able to do stun or curse. Both have 1*,3*, and 5* versions.